Industrial robot

ABSTRACT

An industrial robot including a tool flange at an end of an outer arm of the robot. A tool is secured to the tool flange. A sensor is configured to sense forces and/or torques applied to a tool secured to the tool flange. The sensor is built into the structure of the robot in the region of the tool flange.

TECHNICAL FIELD OF THE INVENTION AND PRIOR ART

The invention relates to an industrial robot having a tool flange at theend of an outer arm of the robot with means for securing a tool theretoand sensor means adapted to sense forces and/or torques applied to atool secured to said tool flange.

All types of industrial robots having a tool flange are comprised. Thistool flange, also called tool attachment, is preferably, but notnecessarily, turnable with respect to said robot arm about a centre axisof said flange.

The number of axis of such an industrial robot is often six forobtaining a maximum freedom of movement of a tool secured to said toolflange. However, the invention also comprises industrial robots havingless than six axis, such as only four, depending upon the work intendedto be carried out by the robot. A conventional robot of this type havingsix axis is by way of example schematically shown in appended FIG. 1, inwhich the six axis are indicated by reference numerals 1-6. Accordingly,in this case the axis number 6 is the one for turning the tool flangearound the centre axis thereof.

Appended FIG. 2 shows how a tool 7 (such as a milling tool shown inFIG. 1) is normally secured directly to said tool flange 8 by securingmeans in the form of bolts 9 and threaded holes 10 in the tool flange.

However, there is sometimes a need to measure forces and/or torquesapplied to a tool secured to said tool flange for ensuring that theforces desired for a good result of a process carried out by the toolare obtained. Such robot applications often are for example differenttypes of assembly work within the fields of electronics and householdappliances, polishing, grinding, for instance of faucets and turbineblades, milling (here also for protecting the tool), cleaning andfriction stir welding, for example within the automotive and aircraftindustries. The sensor means may also be used for measuring forces in aprocess for example for checking resilient details after mounting.

A third possibility is to use the sensor means for protecting an objecthandled by the tool and/or the tool itself. This is especially, but notexclusively, the case when the robot is adapted to handle objects towhich such forces and/or torques have to be kept below comparatively lowlevels. An industrial robot may for example through the tool thereof notapply any substantial forces upon components, such as gear wheels, whenassembling a gearbox, for example for a car. In such a case theindustrial robot has to be provided with a sensor means as defined inthe introduction.

FIG. 3 shows how industrial robots have been provided with such sensormeans so far. The sensor means 11 is secured to the tool flange 8 andthe tool 7 is then secured to the sensor means. Thus, the sensor meansforms an intermediate part between the tool flange and the toolincreasing the torques applied by the tool upon parts of the robot atthe end of said outer arm, such as with respect primarily to said fifthaxis in the case of a robot according to FIG. 1. Thus, the sensor meanssense forces and/or torques applied to the tool flange and by thatindirectly to a tool secured to said tool flange, and this is intendedto be interpreted as the same in this disclosure. This increase indistance between the tool flange and the tool may be even greater thanthe thickness of the sensor means, since adapter discs may be necessaryon both sides of the sensor means for enabling securing thereof to thetool flange and a securing member 12 of the tool. This so-called “addedoffset” causes additional stress on stiffness of robot parts, which isharmful to the accuracy of the tool movements and may by that reduce thework load capacity of the robot. This may result in a cost increase,since a bigger robot may be required. In the worst case such a sensormeans may in fact make the robot application inappropriate orimpossible. Furthermore, sensor means of this type are extremely costlyand constitute a considerable part of the costs of the industrial robotbeing in the same order as the costs for the rest of the structuralparts (the manipulator) of the robot.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an industrial robot ofthe type defined in the introduction reducing the above drawbacks ofsuch robots already known.

This object is according to the invention obtained by providing such anindustrial robot, in which said sensor means is built into the structureof the robot in the region of said tool flange. This means that said“additional offset” for providing the robot with sensor means may beavoided or reduced, so that the workload capacity of the robot may bekept at substantially the same level as for a robot without said sensormeans, so that no bigger robot may be required for handle a given loadwith a predetermined accuracy. Furthermore, no expensive sensor means isrequired, since sensor means built in into the structure of the robotmay be provided at a substantially lower cost than discrete sensor meansused so far (FIG. 3).

According to an embodiment of the invention said sensor means comprisesone or more sensor members built into the tool flange, which constitutesone favourable way of realising the present invention having very littleinfluence upon the construction of the robot.

According to another embodiment of the invention said sensor meanscomprises one or more sensor members arranged on a carrier to which thetool flange is rigidly connected. This alternative arrangement of saidsensor members may under circumstances reduce the impact of thearrangement of the sensor means on the construction of the robot evenless. Said carrier may be an axle pin or the like being integral withthe tool flange. These two embodiments may very well be combined, sothat sensor means may be built into the tool flange as well as arrangedon said carrier.

According to another embodiment of the invention said sensor meanscomprises at least one tensiometer secured to the tool flange or a partrigidly connected thereto. The use of a tensiometer for sensing forcesand/or torques applied to a tool secured to a tool flange results in aremarkable saving of costs with respect to the sensor means used so farwhile maintaining a high reliability. “Tensiometer” is here defined tocover all types of members adapted to measure forces by dilatation orextension of a body, such as wire strain gauges, semiconductor sensors,electro-resistive and piezo-resistive sensors and the like.

According to another embodiment of the invention said sensor meanscomprises a plurality of sensor members for sensing forces and/ortorques according to a plurality of degrees of freedom. A sensor meansdelivering information of an extent desired for the intended applicationof said industrial robot may in this way be obtained by an appropriateselection of the number of said tensiometers, and in a furtherembodiment of the invention said sensor means comprises six sensormembers for sensing and later evaluation of forces according to threedegrees of freedom and torques according to three degrees of freedom, sothat information about all forces and torques acting upon the toolflange and by that upon a said tool may be obtained for enabling amaximum degree of accuracy of the operation of the tool and the objecthandled thereby.

According to another embodiment of the invention said tool flangecomprises a ring provided with said tool securing means and connectedthrough substantially rigid spokes to an inner hub fixed to a carrierconnected to said arm, and said sensor means comprises one or moresensor members arranged on one or more of said spokes. This constitutesa simple way of building said sensor means into the tool flange. Thespokes and by that the sensor members will be influenced by forces andtorques applied to a tool secured to the tool flange, so thatinformation thereabout may be delivered to a unit of the robotcontrolling the movements of the robot. The spokes have of course toprovide a connection between the ring and the hub being rigid, so thatthe accuracy of the operation of the tool will not be lowered therebybut still allowing the tensiometers to be influenced by forces andtorques applied to the tool and being below the levels acceptabletherefore.

According to another embodiment of the invention said sensor meanscomprises at least one sensor member in the form of a tensiometerchanging the resistivity when extended or compressed, and according to astill further embodiment said sensor means comprises at least one sensormember in the form of a piezo resistive element. The use of such sensormembers enables reliable measurements of said forces and torques whilekeeping the costs for the sensor means at an attractive low level.

According to another embodiment of the invention the robot comprises aprinted circuit card built into said tool flange, and sensor members ofsaid sensor means are connected to said printed circuit card fordelivering measurement signals to a unit controlling the operation ofthe robot. Such a printed circuit card may easily be built into the toolflange for facilitating the communication between said control unit andthe sensor means.

The invention also relates to a method and a use according to thecorresponding appended claims.

Other advantage features as well as advantageous of the pre-sentinvention appear from the following description and the other dependentclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings below follows a specificdescription of embodiments of the invention cited as examples. In thedrawings:

FIG. 1 is a simplified perspective view of a known industrial robot towhich the present invention may be applied,

FIG. 2 is a simplified view illustrating a tool flange and partsconnected thereto of an industrial robot already known,

FIG. 3 is a view similar to that of FIG. 2 illustrating the arrangementof sensor means on the tool flange of a robot according to the priorart,

FIG. 4 is a partially sectioned view similar to that of FIG. 2illustrating the region of the tool flange of an industrial robotaccording to a first embodiment of the invention,

FIG. 5 is a view similar to that according to FIG. 4 of the tool flangeregion of an industrial robot according to a second embodiment of theinvention,

FIG. 6 is a partially sectioned view according to VI-VI in FIG. 5,

FIG. 7 is a view similar to that according to FIG. 5 of the tool flangeregion of an industrial robot according to a third embodiment of theinvention,

FIG. 8 is a view similar to that according to FIG. 5 of the tool flangeregion of an industrial robot according to a fourth embodiment of theinvention, and

FIG. 9 is a view similar to that according to FIG. 5 of the tool flangeregion of an industrial robot according to a fifth embodiment of theinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The region of the tool flange in an industrial robot according to afirst preferred embodiment of the invention is schematically illustratedin FIG. 4. The tool flange 8 is an integral part with a carrier 13 inthe form of an axle pin which may be connected to a fork defining theaxis 5 indicated on the robot shown in FIG. 1. The tool flange with thecarrier 13 may have substantially the same shape as for a correspondingrobot having no sensor means. The sensor means comprises sensor members14, 15 in the form of tensiometers arranged on the carrier 13 andadapted to sense forces and/or torques applied to the carrier 13 and bythat to the tool flange 8 and the tool 7. These tensiometers may forexample be silicon strain gauges of the type changing the resistivitywhen extended or compressed or the sensor members may be in the form ofpiezo resistive elements. The sensor members 14, 15 shown in the figuremay for example be adapted to measure forces in directions enablingcalculation of for instance the force on the tool in the directionaccording to the arrow x and the torque with respect to the directionaccording to the arrow y. More sensor members than those shown in thisfigure may be applied to the carrier 13.

The sensor members are connected to an electronic arrangement 16 formingan interface between the sensor members and an output signal to a unit19 controlling the operation of the robot. The electronic arrangementmay be arranged on a printed circuit card built into the tool flange.The printed circuit card and the sensor members may be embedded into aprotecting plastic layer 17. A cable 18 is connected to the electronicarrangement for delivering measurement results from the sensor membersto the control unit 19 schematically indicated controlling the operationof the robot. The sensor means may also be provided with electricalenergy through said cable 18 when necessary.

FIGS. 5 and 6 illustrate a region of the tool flange of an industrialrobot according to a second embodiment of the present invention. Thetool flange 8 is in this embodiment slightly modified with respect to aconventional tool flange by having an outer ring 20 provided with toolsecuring means in the form of threaded holes 10, an inner hub 21 formingsaid carrier of the tool flange in the form of an axle pin as in theembodiment according to FIG. 4, and substantially rigid spokes 22interconnecting the hub and the ring. Sensor members 23-28 are arrangedon the spokes for sensing forces and torques applied to the tool 7secured to the tool flange 8. The sensor members are strain gaugesarranged in couples with an angular distribution around the centre axisof the tool flange of 120° and with the sensors in each couple arrangedperpendicular to each other. The sensor members may in this way senseforces for determining forces according to three degrees of freedom andtorques according to three degrees of freedom, so that all forces andtorques applied on the tool/tool flange may be determined. The spokesand the sensor members are here together with an electronic arrangement16 embedded in a protecting plastic layer 17 as in the embodimentaccording to FIG. 4. Other “deformable” parts than spokes, such as forexample a membrane-like deformation zone, are also possible for theapplication of tensiometers for measuring forces and/or torques.

FIG. 7 illustrates a region of the tool flange of an industrial robotaccording to a third embodiment of the present invention. Thisembodiment differs from that according to FIG. 5 mainly by the fact thatit is provided with an overload protection ensuring that the deformationof the spokes will not exceed a predetermined level. This is ensured byarranging preferably three or more radially extending pins 29 evenlydistributed around the axle 30. These pins are arranged with a play 31with respect to a ring 32 secured to the tool flange 8. This ring 32 isalso arranged with a radial play 33 with respect to the axle 30. Theseplays 31, 33 define the maximum deformation of the tool flange withspokes allowed. The considerably smaller cross-section area of thespokes 22 with respect to the hub 21 results in deformations of the hubbeing neglectable in comparison with deformations of the spokes.

FIG. 8 illustrates a region of the tool flange 8 of an industrial robotaccording to a fourth embodiment of the present invention, in which thesensor members 23-28 (not all of them are visible in the figure) arearranged in a specially designed axle 34. This axle includes sixso-called kinematic links 35 interconnecting the carrier of the toolflange 8 with the axle itself. The sensor members are arranged on thesekinematic links and are through wires 36 connected to a cable 37extending inside the axle 34 to a said control unit of the robot. Acasing 38 is arranged for protecting the link arrangement.

FIG. 9 illustrates a region of the tool flange 8 of an industrial robotaccording a fifth embodiment of the present invention. The axle 39carrying the tool flange 8 is in this case rigidly connected to the toolflange. Six sensor members are arranged in couples with a distributionof 120° inside the bearing housing 40 of the axle for measuringdeformation of the bearing housing and by that determining the forcesand/or torques acting on the axle 39 and by that on the tool.

FIGS. 8 and 9 illustrates that “region” in the expression “sensor meansis built into the structure of the robot in the region of the toolflange” is to be interpreted to also include location of the sensormembers at an end position of an axle carrying the tool flange.

Accordingly, an industrial robot useful for applications requiring forceand/or torque sensors is according to the present invention obtainedwhile saving considerable costs with respect to such robots alreadyknown. Thus, a robot of this type may very well be used for carrying outassembly works within the field of electronics, automotive industry andhousehold appliances. It may also be used for polishing and grindingworks, such as carried out on faucets and turbine blades. Differenttypes of milling and cleaning works are also possible applications.Furthermore, friction stir welding, for example within the automotiveand aircraft industry, are other possible applications.

An example of an application in which it is crucial to prevent an objectfrom being exerted to harmful forces and/or torques has been mentionedabove when discussing the assembly of a gear box. When using anindustrial robot of this type for carrying out milling operations it maybe desired to protect the tool itself from being damaged by restrictingforces and/or torques applied thereon when arriving to for example burrson a work piece being machined.

The invention is of course not in any way restricted to the embodimentsdescribed above, but many possibilities to modifications thereof wouldbe apparent to a person with ordinary skill in the art without departingfrom the basic idea of the invention as defined in the appended claims.

The number of the sensor members and the position thereof may bedifferent than shown in the figures as long as they are built into thestructure of the robot in the region of the tool flange. “Built into thestructure of the robot” means that the sensor means are located withinthis structure and not located externally to this structure by beingarranged between the tool flange and the tool or externally of the toolflange. The sensor members may also comprise tensiometers based oncapacitance changes of semiconductor components.

It is pointed out that “tool flange” is to be interpreted as a toolattachment which may have many different shapes, and it has not to havea circular cross-section. “Ring” as used in the claims and in thedisclosure above does also comprise other shapes than circular, such asdifferent type of polygons, for instance a square.

“Arranged on said spokes” of course also comprises the case of arranginga sensor member partially or totally embedded into a said spoke.

It is also possible to evaluate the torque on the robot arm connectingto the tool flange by measuring the current in an electric motor turningthe tool flange and by that the motor torque.

“Rigidly connected” as used in the description and the claims does notexclude a possibility to disconnect the members thus connected.

An electronic arrangement as shown in FIGS. 4 and 5 may also be arrangedin the other embodiments described above.

1. An industrial robot, comprising: a tool flange at the end of an outerarm of the robot; means for securing a tool to the tool flange; and asensor means adapted to sense forces and/or torques applied to a toolsecured to said tool flange, wherein said sensor comprises one or moresensor members built into the tool flange or arranged on a carrier towhich the tool flange is rigidly connected.
 2. The robot according toclaim 1, wherein said sensor comprises at least one tensiometer securedto the tool flange or a part rigidly connected thereto.
 3. The robotaccording to claim 1, wherein said sensor comprises a plurality ofsensor members for sensing forces and/or torques according to aplurality of degrees of freedom.
 4. The robot according to claim 3,wherein the sensor comprises six sensor members for sensing and laterevaluation of forces according to three degrees of freedom and torquesaccording to three degrees of freedom.
 5. The robot according to claim1, wherein said tool flange comprises a ring provided with said toolsecuring means and connected through substantially rigid spokes to aninner hub fixed to a carrier connected to said arm, and wherein saidsensor comprises one or more sensor members arranged on one or more ofsaid spokes.
 6. The robot according to claim 1, wherein said sensormeans comprises at least one sensor member in the form of a tensiometerchanging the resistivity when extended or compressed.
 7. The robotaccording to claim 1, wherein said sensor means comprises at least onesensor member in the form of a piezo resistive element.
 8. The robotaccording to claim 1, further comprising: an electronic arrangementbuilt into said tool flange, wherein sensor members of said sensor areconnected to said electronic arrangement for delivering measurementsignals to a unit controlling the operation of the robot.
 9. The robotaccording to claim 8, further comprising: a cable configured to connectsaid electronic arrangement to said control unit.
 10. The robotaccording to claim 1, wherein said tool flange is arranged to be turnedwith respect to said robot arm about a centre axis of said flange. 11.The method for sensing forces and/or torques applied to a tool securedto a tool flange of an industrial robot, the method comprising:measuring deformation of a bearing housing for an axle rigidly connectedto the tool flange to determine the forces and/or torques acting on saidaxle and thereby the forces and/or torques acting on the tool.
 12. Useof a tensiometer for sensing forces and/or torques applied to a toolsecured to a tool flange of an industrial robot.